This invention relates to an apparatus for encoding a speech signal, and also relates to a decoding apparatus matching the encoding apparatus.
Apparatus for encoding a speech signal at a low bit rate of about 4.8 kbps is usually one of two types, that is, a speech analysis and synthesis encoding type and a speech waveform encoding type. In the first type, frequency characteristics of a speech are extracted by a spectrum analysis such as a linear predictive analysis, and the extracted frequency characteristics and speech source information are encoded. In the second type, a redundancy of a speech is utilized and a waveform of the speech is encoded.
Prior art encoding of the first type is suited to the realization of a low bit rate but is unsuited to the encoding of a drive speech source for synthesizing a good-quality speech. On the other hand, prior art encoding of the second type is suited to the recovery of a good-quality speech but is unsuited to the realization of a low bit rate. Thus, either the prior art encoding of the first type or the prior art encoding of the-second type requires a compromise between a good speech quality and a low bit rate.
Further, either the prior art encoding of the first type or the prior art encoding of the second type tends to make processing complicated and thus to increase calculation steps.